This invention relates to a method for detecting and measuring volatile components of expired gas by the use of low resolution Fourier transformed infrared (FT-IR) spectrometry.
Drugs and alcohols account for the majority of acute intoxications treated in hospitals. In many cases drugs and alcohols are ingested together. Symptoms are often non-specific and the intoxication diagnosis is largely based on anamnesis. While anamnesis is often uncertain and confusing, fast and reliable diagnostic methods are needed. Present laboratory methods, however, seldom reveal quickly and accurately the intoxicant and its amount in the body. To detect, and more often to exclude, substances that necessitate immediate special and expensive treatment (e.g. dialysis in the case of methanol intoxication) is important as soon as possible.
Expired human breath contains a number of components that may give valuable information of metabolic processes and substances in blood because only a slender barrier separates air in the alveoli of the lung from the blood in the capillaries. Any volatile compound, such as alcohols, diffuse across the alveolar membrane from the compartment with the higher vapor pressure to the lowerxe2x80x94from the blood into the air, or vice versa use (Phillips 1992).
There are few analytical methods with which one can perform real-time identification and quantification of the components of the expired air. Except measuring breath ethanol concentrations of drunken drivers, methods available at present require collecting and concentrating the breath samples before analyzing and are more or less impractical for clinical use (Phillips 1992). At present, instruments that come closest to fulfill the idea of direct identification and of quantification expired breath are based on either infrared (IR) spectroscopy or mass spectrometry (MS).
Since mid 1980""s, IR-techniques have been applied for breath ethanol testing. The instruments used have been made more specific for alcohol by using several optical IR-filters or using electrochemical sensors as a second independent detector (Jones et al. 1996). Infrared spectroscopy is one of the fastest methods to analyze gas mixtures. A quantitative infrared analysis of one or few components in a gas mixture is a relative simple task if an isolated absorption peak can be found for each component. Difficulties arise if the characteristic peaks of the compounds overlap, or unknown compounds exist. In these cases laborious methods like gas chromatography have been used. More recently, the problems of spectral overlap have been attacked by applying chemometric methods such as classical least square methods to digitized Fourier transformed IR-spectral (FT-IR) data (Jaakkola et al. 1997).
U.S. Pat. No. 5,313,406 (Kauppinen et al. 1994) describes procedures for analyzing multicomponent FT-IR spectra for unknown mixtures of gases.
The object of the present invention is to provide a method for detecting and measuring volatile components in expired gas.
The invention provides a method for detecting and measuring volatile components in expired gas by
sampling the expired gas containing said volatile components;
passing infrared radiation from an interferometer through the sample;
detecting infrared radiation transmitted from the sample to produce a signal characteristic for said volatile components in the sample; and
processing said signal and a set of single component reference library spectra of pure molecular gases in order to detect and calculate the amount of said volatile components in the blood of an individual expiring said gas, comprising the use of a low resolution FT-IR spectrometer in said detecting and processing.
The invention explicitly provides a method that makes use of low resolution FT-IR in the mid infrared range and reference libraries comprising gases that would or could be included in the composition of expired breath and said method thus also provides a method that is applicable for the detecting and measuring of volatile components in expired gas using apparatus of reasonable cost and suitable for ambulatory use.